DIRBE-based zodiacal spectrum subtracted

In the wavelength range of PHT-S the dominant background component is the zodiacal light (apart from localised regions like HII regions, reflection nebulae, or the galactic plane). In the 5.8-11.7 um regime the zodiacal flux was clearly measurable for PHT-S (see Leinert et al., 2002), and its contribution is not negligible in the case of fainter stars (Figure 1). We created a model which was able to predict the spectrum of the zodiacal background towards a given direction and on a given date. The algorithm used 4.8 and 12 um photometric points from COBE/DIRBE photometry as input; connected them with a Planck-curve; and finally scaled with a wavelength- and observing time-dependent factor optimized for the 29 high quality PHT-S spectra of the Zodiacal Light presented in Leinert et al. (2002). When no dedicated sky background measurement was performed by the observer, this predicted zodiacal light spectrum was subtracted from the on-target spectrum as part of our processing scheme.

Fig.1: Contribution of the zodiacal background to the measured flux of BF Ori. Since no dedicated background measurement was performed, the zodiacal spectrum was estimated from the DIRBE 4.9 and 12 um data points extracted for the position and date of the BF Ori observation.